The present invention relates to a laser device, in particular, a laser device used in an ophthalmological surgical system such as a photocoagulator. Also, the invention relates to an ophthalmological surgical system equipped with the laser device.
In recent years, a type of ophthalmological surgical system has been propagated, by which it is possible to perform photocoagulation, resection, incision, etc. of a site to be treated on non-contact basis by using high energy density of a laser beam and operation can be performed by preventing hemorrhage and without risk of contamination with bacteria.
In the ophthalmological surgical system using a laser beam, a laser beam is projected to a site to be treated through a pupil of a human eye, and the procedures such as photocoagulation, resection, incision, etc. can be carried out.
FIG. 4 is a schematical drawing of a photocoagulator. In the figure, reference numeral 1 denotes a laser device, 2 is a condenser lens, 3 is an optical fiber for guiding a laser beam to a target position, 4 is a condenser lens, 5 is a human eye, and 6 represents a pupil of an eye.
A laser beam 10 with an opening angle θ emitted from the laser device 1 is converged by the condenser lens 2 and enters the optical fiber 3. The opening angle θ can be approximated to numerical aperture NA. In the following, description will be given by referring the opening angle as numerical aperture NA. The laser beam 10 enters the optical fiber 3 with numerical aperture NAi. The laser beam 10 is emitted from the optical fiber 3 with numerical aperture NAe. Further, the laser beam 10 is converged by the condenser lens 4 and is projected to the human eye 5. Among the light components of the laser beam 10 converged by the condenser lens 4, the light components corresponding to numerical aperture NAm of the pupil 6 are projected to an eye fundus of the human eye 5, and photocoagulation is performed on an affected site.
FIG. 5 shows relation of numerical aperture NAi of the laser beam 10 entering the optical fiber 3, numerical aperture NAe of the laser beam 10 emitted from the optical fiber, and numerical aperture NAf of the optical fiber 3. These numerical apertures have a relation of: NAi<NAe<NAf.
In the photocoagulator as described above, if the laser beam 10 emitted from the optical fiber 3 is directly projected to the human eye 5, the numerical aperture of the pupil 6 is: NAm≦0.06. The numerical aperture of the optical fiber 3, from which the laser beam 10 is emitted, is: NAf=0.12. Therefore, when the numerical aperture of the laser beam 10 entering the optical fiber 3 is big, the numerical aperture of the laser beam 10 emitted from the optical fiber 3 is also increased more compared with the numerical aperture NAm of the pupil 6.
When the laser beam 10 emitted from the optical fiber 3 projects an optical fiber image to a retina in equal size or in reduced size and photocoagulation is performed, peripheral portion of the laser beam 10 is interrupted by the pupil 6 as shown in FIG. 4. Only the luminous flux near the center of the laser beam 10 can be projected to the eye fundus, and optical loss is extremely increased. No trouble occurs if the laser beam 10 emitted from the laser device 1 has sufficient light amount. However, in case a semiconductor laser is used as a light source of the laser device 1, it is difficult to have higher light amount of the laser beam 10 to reach the eye fundus, and it is not easy to have the light amount sufficient for the treatment.
If the numerical aperture NAi of the laser beam 10 entering the optical fiber 3 is decreased, the numerical aperture NAe of the exit laser beam 10 is also decreased, and the loss of the laser beam projected to the eye fundus through the pupil 6 can be decreased. Therefore, it is generally practiced to project the laser beam to the optical fiber 3 by decreasing the numerical aperture NAi of the laser beam 10 emitted from the laser device 1.
However, when the numerical aperture of the laser beam 10 to enter the optical fiber 3 is decreased, light intensity distribution at a projected point is made uneven due to interference between propagation modes excited when the laser beam 10 passes through the optical fiber 3. FIG. 6(C) and FIG. 6(D) show the conditions of the laser beam 10 at the projected point in condition that interference occurs. FIG. 6(A) and FIG. 6(B) show the light intensity of the laser beam 10 is uniform, and light intensity distribution is in form of a top hat. When these two cases are compared with each other, speckled spots are seen at the projected point in case of the laser beam 10 with interference, and it is apparent that there is extreme variation in the light intensity distribution. When photocoagulation operation is performed, the speckled spots at the projected point and light intensity distribution of the laser beam 10 exert influence on the therapeutic effects.
For this reason, it has been practiced in such manner that the laser beam emitted from the optical fiber has uniform light intensity by using optical members such as a micro lens array, an axicon lens etc. This is described, for instance, in: CLEO 2001, Short Course Notes, SC117, Laser Beam Analysis, Propagation, and Shaping Techniques, written by James R. Leger, published on May 7, 2001.
A simple method is known, by which focus is not formed on a retina but it is turned to de-focused state, and non-uniformity of the light intensity is averaged. This is described, for instance, in JP-A-8-196561.
In the conventional method as described above, which uses optical members such as a micro lens array, an axicon lens, etc. to equalize the light intensity, many component parts are required and this leads to higher cost. In the method to turn to de-focused state and to equalize and average the non-uniformity of the light intensity, there has been problems such that it is difficult to maintain the de-focused state.